dt-binding: clk: add clock binding docs for Marvell Berlin2 SoCs

This adds mandatory device tree binding documentation for the clock related
IP found on Marvell Berlin2 (BG2, BG2CD, and BG2Q) SoCs.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>

diff --git a/Documentation/devicetree/bindings/clock/berlin2-clock.txt b/Documentation/devicetree/bindings/clock/berlin2-clock.txt
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+* Marvell Berlin2 clock bindings
+
+Marvell Berlin2 (BG2, BG2CD, BG2Q) share the same IP for PLLs and clocks,
+with some minor differences in features and register layout. The below
+describes the individual clock related IP:
+
+* Audio/Video PLL
+
+The Audio/Video PLL (AVPLL) is a dual-VCO PLL with 8 channels each. Each
+of the VCOs can sythesize a single VCO frequency based on a single input
+reference clock. Each of the 8 channels then, can derive an output clock
+from that VCO frequency by various dividers/multipliers.
+
+Required properties:
+- compatible: shall be "marvell,berlin2-avpll"
+- reg: address and length of the corresponding AVPLL registers
+- #clock-cells: shall be set to 2
+- clocks: single clock specifier referencing the AVPLL input clock
+
+To ease match-up with the desired AVPLL output clock, clock specifiers
+referencing AVPLL clocks shall contain two cells. The first refers to
+the VCO (0=AVPLL_A, 1=AVPLL_B) while the second refers to the corresponding
+channel starting with 1. For example, to reference AVPLL_B3 the clock
+specifier shall be: <&avpll 1 3>.
+
+Example:
+
+avpll: pll@ea0040 {
+       compatible = "marvell,berlin2-avpll";
+       #clock-cells = <2>;
+       reg = <0xea0050 0x100>;
+       clocks = <&refclk>;
+};
+
+* Simple PLLs
+
+Simple PLLs are memory mapped PLLs that can sythesize a single output clock
+based on a single input reference clock.
+
+Required properties:
+- compatible: shall be one of the following:
+       "marvell,berlin2-pll" for Berlin BG2/BG2CD PLLs
+       "marvell,berlin2q-pll" for Berlin BG2Q PLLs
+- reg: address and length of the corresponding PLL registers
+- #clock-cells: shall be set to 0
+- clocks: single clock specifier referencing the PLL input clock
+
+Example:
+
+cpupll: pll@ea003c {
+       compatible = "marvell,berlin2-pll";
+       #clock-cells = <0>;
+       reg = <0xea003c 0x14>;
+       clocks = <&refclk>;
+};
+
+* Single-register clock dividers
+
+Single-register clock dividers are complex divider cells, allowing
+to divide a reference clock with a set of fixed dividers. Also they
+comprise and input clock mux with bypass and an ouput clock gate.
+
+Required properties:
+- compatible: shall be "marvell,berlin2-clk-div"
+- reg: address and length of the corresponding DIV registers
+- #clock-cells: shall be set to 0
+- clocks: clock specifiers referencing the DIV input clocks
+- clock-names: array of strings describing the clock specifiers above.
+    Allowed clock-names are "mux_bypass" for the clock mux bypass selection
+    and "muxN" (N=0..7) for each of the 8 possible clock mux inputs.
+
+Example:
+
+gfx3dcore_clk: clock@ea022c {
+       compatible = "marvell,berlin2-clk-div";
+       #clock-cells = <0>;
+       reg = <0xea0022c 0x4>;
+       clocks = <&syspll>,
+               <&avpll AVPLL_B 4>, <&avpll AVPLL_B 5>,
+               <&avpll AVPLL_B 6>, <&avpll AVPLL_B 7>;
+       clock-names = "mux_bypass",
+               "mux0", "mux1", "mux2", "mux3";
+};
+
+* SoC-specific core clocks
+
+In addition to the above, there is a register set dealing with SoC
+specific clock dividers, muxes, and gates. There is also the complex
+divider cell used above, but instead of independent registers, they
+share a common set of registers. The core clocks are represented by
+a single DT node providing access to the remaining clocks.
+
+Required properties:
+- compatible: shall be one of
+       "marvell,berlin2-core-clocks" for BG2/BG2CD SoCs
+       "marvell,berlin2q-core-clocks" for BG2Q SoCs
+- reg: address and length of the corresponding clock registers
+- #clock-cells: shall be set to 1
+- clocks: clock specifiers referencing the core clock input clocks
+- clock-names: array of strings describing the clock specifiers above.
+    Allowed clock-names for the reference clocks are
+      "refclk", "syspll", "mempll", "cpupll"
+    also Audio/Video PLL clocks shall be named with
+      "avpll_VN" (V=0...1 for AVPLL_A and AVPLL_B, N=1..8 for the
+      corresponding reference input from AVPLL).
+
+Optional properties for BG2/BG2CD SoCs:
+- clocks/clock-names: in addition to the allowed clock names above,
+    there is an external video clock input that shall be named "video_ext0".
+
+Clocks provided by core clocks shall be referenced by a clock specifier
+indexing one of the provided clocks. A SoC-specific list of available clocks
+is below the example.
+
+Example:
+coreclk: clock@ea0150 {
+       compatible = "marvell,berlin2-core-clocks";
+       #clock-cells = <1>;
+       reg = <0xea0150 0x1c>;
+       clocks = <&refclk>, <&syspll>, <&mempll>, <&cpupll>,
+               <&avpll 0 1>, <&avpll 0 2>,
+               <&avpll 0 3>, <&avpll 0 4>,
+               <&avpll 0 5>, <&avpll 0 6>,
+               <&avpll 0 7>, <&avpll 0 8>,
+               <&avpll 1 1>, <&avpll 1 2>,
+               <&avpll 1 3>, <&avpll 1 4>,
+               <&avpll 1 5>, <&avpll 1 6>,
+               <&avpll 1 7>, <&avpll 1 8>,
+               <&externalvideoclk>;
+       clock-names = "refclk", "syspll", "mempll", "cpupll",
+               "avpll_a1", "avpll_a2", "avpll_a3", "avpll_a4",
+               "avpll_a5", "avpll_a6", "avpll_a7", "avpll_a8",
+               "avpll_b1", "avpll_b2", "avpll_b3", "avpll_b4",
+               "avpll_b5", "avpll_b6", "avpll_b7", "avpll_b8",
+               "video_ext0";
+};
+
+* BG2/BG2CD core clock indicies:
+0  - SYS
+1  - CPU
+2  - DRMFIGO
+3  - CFG
+4  - GFX
+5  - ZSP
+6  - PERIF
+7  - PCUBE
+8  - VSCOPE
+9  - NFC_ECC
+10 - VPP
+11 - APP
+12 - AUDIO0
+23 - AUDIO2
+14 - AUDIO3
+15 - AUDIO1
+16 - GETH0
+17 - GETH1
+18 - SATA
+19 - AHBAPB
+20 - USB0
+21 - USB1
+22 - PBRIDGE
+23 - SDIO0
+24 - SDIO1
+25 - NFC
+26 - SMEMC
+27 - AUDIOHD
+28 - VIDEO0
+29 - VIDEO1
+30 - VIDEO2